HESI A2 Anatomy and Physiology Quizlet

Correct Answer: A

Rationale: The correct answer is A: Melatonin. Melatonin is a hormone produced by the pineal gland that plays a key role in regulating the sleep-wake cycle. It helps control the body's internal clock and signals the brain when it's time to sleep. Melatonin levels typically rise in the evening, promoting sleep, and decrease in the morning, promoting wakefulness. Summary of incorrect choices: B: Insulin - Insulin is a hormone that regulates blood sugar levels, not the sleep-wake cycle. C: Cortisol - Cortisol is a stress hormone that helps regulate metabolism and immune response, but it does not directly control the sleep-wake cycle. D: Thyroxine - Thyroxine is a hormone produced by the thyroid gland that regulates metabolism, growth, and development, but it is not directly involved in the sleep-wake cycle regulation.

Correct Answer: C

Rationale: The correct answer is C: Smooth muscle. Smooth muscle tissue is found in the walls of hollow organs such as the intestines, blood vessels, and bladder. It is involuntary, non-striated, and capable of sustained contractions. Skeletal muscle (A) is attached to bones and is under voluntary control. Cardiac muscle (B) is found in the heart and has a unique branching structure. Striated muscle (D) includes both skeletal and cardiac muscle, but smooth muscle specifically lines hollow organs.

Correct Answer: C

Rationale: The correct answer is C: Medulla oblongata. The medulla oblongata is located in the brainstem and is responsible for controlling vital functions such as breathing, heart rate, and blood pressure. It contains important centers that regulate these involuntary actions, making it the correct choice. The cerebrum (A) is responsible for higher brain functions such as thinking and voluntary movement. The cerebellum (B) is involved in coordination and balance. The hypothalamus (D) regulates body temperature, hunger, and thirst, but does not directly control breathing and heart rate.

Correct Answer: B

Rationale: The correct answer is B: Lens. The lens is responsible for focusing light onto the retina by adjusting its shape to bend the light rays. The cornea (A) primarily helps in refracting light, while the pupil (C) and iris (D) are involved in regulating the amount of light entering the eye, not in focusing light onto the retina. Therefore, the lens is the correct choice as it plays a crucial role in the process of focusing light onto the retina.

Correct Answer: A

Rationale: The correct answer is A: Hemoglobin. Hemoglobin is a protein in red blood cells that binds to oxygen in the lungs and carries it to the body's tissues. Plasma is the liquid component of blood and does not directly carry oxygen. Platelets are responsible for blood clotting, not oxygen transport. Red blood cells contain hemoglobin and are the primary carriers of oxygen, making them indirectly responsible for carrying oxygen. However, the specific structure responsible for carrying oxygen is hemoglobin within red blood cells.